The present invention relates to a shutter for a camera having a motor for effecting opening and closing of a set of shutter sectors, and more particularly to a shutter for a camera in which forward and reverse pulses are applied to the motor to prevent rebounding motion of the sectors.
In a shutter for a camera having a motor or actuator for rotating a rotor formed of a permanent magnet by conducting electricity to a coil and opening and closing a shutter opening by operating a plurality of sectors driven by the motor, it is well known that at a position at which the sectors are fully opened or a position at which the sectors are completely closed, the actual positions of the sectors differ from desired positions thereof due to the inertia of the moving parts including the rotor, the sectors, and the like. This is commonly referred to as the bounding or rebounding phenomenon. The drawbacks associated with rebounding motion include the possibility that portions of the sectors remain covering the shutter opening after the sectors are intended to be fully opened, or re-exposure may be caused after the sectors are intended to be fully closed.
Conventionally, these drawbacks have been resolved by opening the sectors beyond the shutter opening or by closing the sectors to a greater degree than otherwise necessary to avoid the influence of rebounding of the sectors.
According to one such conventional method for overcoming the rebounding phenomenon, an outer diameter of the shutter is increased by a given amount to avoid rebounding of the sectors. However, this creates the problem that a small-sized shutter opening becomes difficult to obtain. Further, even if the sectors have been fully opened, the timing at which the sectors are to be shifted to a closing operation may nonetheless be affected by the rebounding phenomenon and a normal exposure operation may be hampered.
In order to resolve the above-described problems, after finishing a shutter opening operation and a shutter closing operation of the sectors, current is applied to a coil of the motor for a short period of time to rotate a rotor of the motor in a direction reverse to a rebounding direction of the sectors and rotation of the rotor is decelerated to reduce the rebounding motion of the sectors as much as possible.
According to an aspect of the invention, there is provided a shutter for a camera comprising a shutter opening, sectors for opening and closing the shutter opening by reciprocal pivotal movement, a motor for reciprocally and pivotally moving the sectors by forwardly and reversely rotating a rotor by application of forward and reverse currents to a coil disposed around the rotor, a memory circuit for storing electrical conduction data used for exciting the coil and corresponding to operational characteristics of the motor and the sectors, and a control circuit for controlling the application of current to the coil in accordance with the electrical conduction data and the brightness of an object to be photographed and executing exposure control in accordance with the brightness of the object, wherein the electrical conduction data comprises driving pulses for driving the sectors in a forward and reverse directions and brake pulse data used for generating braking pulses for exerting a force on the sectors in a direction opposite a direction of a rebounding motion of the sectors near or after completion of opening and closing operations of the sectors, and the control circuit outputs a control signal for controlling the application of electricity to the coil be reading specific electrical conduction data from the memory circuit in accordance with the brightness of the object to be photographed.